1. Field of the Invention
The present invention relates to an optical disk apparatus and, more particularly, to an optical disk apparatus which, in a recording process, calculates a recording waveform compensation amount and compensates a recording waveform pulse in accordance with the calculated amount.
2. Description of the Related Art
Recently, optical disk apparatuses for performing recording and reproduction with respect to optical disks such as a DVD (Digital Versatile Disc) have been widely used and are developed and manufactured by various specifications. Under the circumstances, it is being desired to improve the performance of the recording waveform pulse compensation technology which changes recording characteristics in accordance with the characteristics of each individual optical disk.
A conventional optical disk system, irrelevant to the present invention, which performs recording waveform pulse compensating process generally comprises a motor for rotating an optical disk at a predetermined rotating speed, a pickup for emitting and receiving a laser beam, a recording means reproducing means, a parameter calculating means, and a recording waveform pulse position/width control means. In this optical disk system, information recorded on an optical disk is reproduced as a weak analog signal by using a pickup head. This analog signal is amplified to a sufficient signal level by a preamplifier and converted into a binary signal corresponding to a mark/space by a level slicer. A PLL (Phase Lock Loop) circuit generates a channel clock whose phase is synchronized with the input binary signal.
By using these binary signal and channel clock signal, a waveform compensation amount before the mark is obtained. On the basis of this compensation amount, the recording waveform pulse position/width control means generates a recording waveform pulse having a recording waveform which does not cause any heat interference at the corresponding space length, thereby recording predetermined data with appropriate characteristics.
Unfortunately, this conventional optical disk apparatus includes a waveform correction amount calculator (parameter calculator) which uses a level slicing method as an identification method. Therefore, if a digital method such as a PRML (Partial Response and Maximum Likelihood) method is used as an identification method, the above conventional method cannot calculate a waveform correction amount.
The PRML method is described in U.S. Pat. No. 6,148,043. However, this reference does not disclose any practical method by which the PRML method is applied to an optical disk recording process. That is, the reference cannot realize an optical disk recording/reproducing process using the PRML method.